The present invention relates to the conversation device of an MR imaging apparatus, and more particularly to the conversation device of an MR imaging apparatus capable of carrying out conversations between a person to be inspected who is placed in a static magnetic field which produces a harsh noise, and an operator who is placed outside of the static magnetic field.
The conversation device of a conventional MR imaging apparatus employs a microphone which is operated by the vibration of air, in order for a to-be-inspected person who is placed in the static magnetic field of the MR imaging apparatus in a state that the to-be-inspected person lies on his or her back, to talk to an operator placed in an operation room.
The above-mentioned prior art, however, has the following drawback. A large current is instantaneously supplied to a coil which is placed in the static magnetic field of the MR imaging apparatus to generate a gradient magnetic field, and thus the coil vibrates. Noise generated by the vibration of the coil is propagated together with the voice of the to-be-inspected person. Further, even when the to-be-inspected person does not talk, the noise due to the vibration of the coil is propagated.
Since the to-be-inspected person is placed in a magnetic field, a microphone utilizing electromagnetic action is disadvantageous in that the microphone is affected by the magnetic field. A condenser microphone is advantageous in that the microphone is not affected by a magnetic field, but such a microphone cannot remove noise due to the vibration of a coil for generating a gradient magnetic field.
A microphone insensitive to surrounding noise has been known which is called a bone conduction microphone. In more detail, the skull of a person is vibrated by the voice of the person, and the vibration of the skull is detected by the bone conduction microphone inserted into an earhole. Alternatively, the vibration of the nasal bone due to the voice of a person is detected by the bone conduction microphone mounted on the frame of spectacles. Such a voice detecting system and bone conduction microphone are described in a catalog of articles for sale of Pilot Electronics Co. Ltd., by the name of a wireless guide system or ear communication system and an eyeglass microphone. The present inventors have made tests of such a bone conduction microphone, and have confirmed that the bone conduction microphone is not affected by a magnetic field.
The bone conduction microphone inserted into an earhole, however, has the following drawbacks. That is, a person to be inspected may forget to insert the microphone into an earhole of the person. Further, the microphone may slip out of the earhole in the course of inspection.